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DNA Replication Essentials
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1
Question
What is the primary purpose of DNA replication?
Answer
To allow cells to replicate and produce identical daughter cells during the cell cycle.
2
Question
During which phase of the cell cycle does DNA replication primarily occur?
Answer
S phase.
3
Question
What does semi-conservative replication mean in DNA?
Answer
Each new double-stranded DNA molecule consists of one old (parental) strand and one new (daughter) strand.
4
Question
In which direction is new DNA always synthesized during replication?
Answer
5' to 3' direction.
5
Question
Why must DNA synthesis occur only from 5' to 3'?
Answer
Nucleotides are added by linking the 5' phosphate of the incoming nucleotide to the 3' OH of the growing strand.
6
Question
What is the term for the Y-shaped regions formed during DNA unwinding?
Answer
Replication forks.
7
Question
How does DNA replication proceed from the origin?
Answer
Bi-directionally from replication forks moving outward.
8
Question
What are the three main stages of DNA replication?
Answer
Initiation, elongation, termination.
9
Question
What feature makes the origin of replication easier to unwind?
Answer
High concentration of adenine-thymine (AT) base pairs.
10
Question
Why are AT-rich regions preferred for the origin over GC-rich?
Answer
AT pairs have 2 hydrogen bonds, requiring less energy to separate than 3 in GC pairs.
11
Question
How many origins of replication are there in eukaryotic cells?
Answer
Multiple origins of replication.
12
Question
What binds to the AT-rich origin to initiate separation?
Answer
Pre-replication protein complex.
13
Question
What structure forms after the pre-replication complex separates strands at the origin?
Answer
Replication bubble.
14
Question
What are the two main functions of single-stranded binding (SSB) proteins?
Answer
Prevent re-annealing of parental strands and protect from nucleases.
15
Question
What enzyme unwinds DNA at the replication forks?
Answer
Helicase.
16
Question
What energy source does helicase require?
Answer
ATP.
17
Question
What problem arises ahead of the replication fork due to helicase activity?
Answer
Supercoils (overwinding) form distal to the fork.
18
Question
What enzymes relieve supercoils during replication?
Answer
Topoisomerases.
19
Question
How do topoisomerases relieve supercoils?
Answer
Nuclease domain cuts strand(s), allows unwinding, ligase domain reseals.
20
Question
Which topoisomerase types are in eukaryotic cells?
Answer
Type 1 and Type 2.
21
Question
Which topoisomerase types are in prokaryotic cells?
Answer
Type 2 and Type 4.
22
Question
Does Type 1 topoisomerase require ATP?
Answer
No.
23
Question
Do Type 2 and 4 topoisomerases require ATP?
Answer
Yes.
24
Question
What eukaryotic Topo I inhibitors are used in cancer chemotherapy?
Answer
Irinotecan and topotecan.
25
Question
What eukaryotic Topo II inhibitors are used in cancer chemotherapy?
Answer
Etoposide and teniposide.
26
Question
What class of drugs inhibits bacterial Topo II/IV?
Answer
Fluoroquinolones (e.g., ciprofloxacin, levofloxacin).
27
Question
How do topoisomerase inhibitor drugs work?
Answer
Enhance nuclease domain activity while inhibiting ligase domain, causing DNA fragmentation.
28
Question
What enzyme synthesizes RNA primers during elongation?
Answer
Primase.
29
Question
In which direction does primase read the template DNA?
Answer
3' to 5'.
30
Question
In which direction does primase synthesize RNA primers?
Answer
5' to 3'.